The invention relates to a method and apparatus for removing liquid condensate from a small volume compressed air system for automotive vehicle door closing systems and the like.
A closing apparatus having a pneumatic auxiliary closing system is known from German Patent Document DE 37 10 347 Al, which assists a vehicle user when closing and opening the doors of his vehicle. A single double-acting actuator having two working chambers is assigned in each case to a reversible pneumatic pump, which for assisting door closure and for assisting door opening is subjected on the one hand to positive pressure and on the other hand to a vacuum, in each case by a correspondingly reversed direction of delivery of the pump, the actuator performing mechanical work in both directions of movement.
Evacuation of the pneumatic system to remove liquid condensate is not disclosed there and is not possible either, because, on the one hand, relatively high positive pressures have to be built up and, on the other hand, the pump running times are in each case limited to the period of time absolutely necessary for performing the mechanical work. Furthermore, the auxiliary closing system can only be switched on the basis of a request for closing or opening assistance.
A compressed-air system with a continuously operating pressure generator is known from German Patent Document DE 32 03 152 A1, which has an air reservoir, an air drier and a regeneration device for the latter. The regeneration device can be connected by a switchable valve to the vacuum side of a venturi nozzle through which the compressed-air stream for idling flows, in order, for the purpose of improving the result of regeneration, to increase the pressure difference between the pressure of the air in the dry phase and the pressure of the regeneration air. The known arrangement contains a relatively large number of valves. For reverse-flow regeneration of the air drier, compressed air from the reservoir must also be available at all times since the relatively low vacuum produced at the venturi nozzle is not sufficient on its own for condensate evaporation.
It is generally known that in pneumatic systems which are alternately subjected to positive air pressure and to atmospheric pressure that water of condensation can precipitate on the inner walls of the system components if, due to the positive air pressure, the water-vapor saturation line of the air at the prevailing temperature is exceeded. This is a result of the physical fact that air can isothermally absorb more water molecules per unit volume at low pressure than at high pressure. A subsequent letting down of the system pressure to atmospheric level does not necessarily bring about the complete re-evaporation of the condensate into the air remaining in the system, resulting in problems, especially at temperatures below the freezing point.
A washing drier is furthermore known from German Patent Document DE 33 21 245 A1, the drying space of which can be evacuated by means of a water jet pump in order to assist the evaporation of the residual moisture. Subjection of the drying space to positive pressure and positive pressure consumers are not envisaged there.
It is an object of the invention, starting from the generic compressed-air system, to specify a method by which water of condensation can be removed in a simple but reliable manner from the system, which is alternately subjectable to pneumatic positive pressure and not subjected to pneumatic positive pressure and, in the state of rest, is under atmospheric pressure, and to at least modify a device of the generic type with a view to carrying out the method according to the invention.
This object is achieved according to preferred embodiments of the invention by providing a system and operating method for removing condensation from a compressed-air system of the type which is subjected to pneumatic positive pressure during a mechanical work performing operation and is vented to ambient atmospheric pressure when not performing mechanical work, said method comprising:
subjecting the compressed-air system to vacuum pressures below atmospheric pressure immediately following work performing operations to thereby cause condensation in the compressed-air system to vaporize.
The water of condensation which has precipitated during the subjection of the system to positive pressure on the inner walls of its components evaporates rapidly again if the system is temporarily subjected to a vacuum immediately after being subjected to a positive pressure. Only after this temporary evacuation is the compressed-air system returned to its state of rest with atmospheric pressure.
This method is particularly suitable for use in small-volume compressed-air systems in which the consumers can be connected directly to a positive pressure/vacuum generator via lines and do not have to be subjected continuously to positive pressure, e.g. in pneumatic door-closing aids for motor cars.
The subjection of the compressed-air system to a vacuum according to the invention can be performed at relatively large intervals--in the case of low incidence of condensate in a dry environment--or after each subjection to positive pressure in damper environments.
An arrangement for controlling a dual pressure pump of an electropneumatic central locking system of a motor vehicle is also described in German Patent Document DE 36 41 276 A1 which, after each operating cycle, drives the dual pressure pump at rated speed in the opposite direction of rotation to that previously in order to bring the system pressure rapidly back to atmospheric level. In a system of this kind, water of condensation does not occur in damaging amounts due to the low positive pressures. Subjection of the system to a vacuum by the dual pressure pump is only provided for the purpose of initiating an actuating procedure of the lock actuating elements opposite to that in the case of subjecting to positive pressure, with the result that the dual pressure pump must be switched off in good time during the reversed operation following subjection to positive pressure to ensure that no undesired actuating procedure occurs due to subjection to a vacuum.
In contrast to the arrangement described in German Patent Document DE 36 41 276 A1, the vacuum of a dual pressure pump in an embodiment of the device according to the invention is not employed for an actuating operation but simply for drying air or evaporating condensate. Of course such a procedure is only sensible if no undesired actuating operations can occur due to subjection of actuating elements present in the compressed- air system to a vacuum.
In certain preferred embodiments, a dual reversible pump is used for generating both positive and vacuum pressure with resultant advantages due to the economy and simplicity of design. In other preferred embodiments, separate electric pumps are provided for producing the positive and vacuum pressures, with resultant advantages for effecting reverse flow to enhance removal of condensation from the system. The present invention also contemplates a special pressure consumer construction with a lip seal and housing valve controls accommodating the operation thereof in conjunction with the vacuum supply for condensate removal operations.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.